Abstract
Surface potential is a key parameter in evaluating the DC property of thin-film transistors (TFTs). In this paper, for the junctionless symmetric double-gate polysilicon TFTs, a physical-based explicit calculation to surface potential has been derived. Incorporating impurity concentration, mobile charge and trap density into Poisson's equation, a closed form of band bending as a function of gate voltage is obtained and demonstrated as an accurate and computationally efficient solution. Based on surface potential, a drain current model for long-channel devices is provided in explicit forms. Furthermore, it is verified successfully by comparisons with both 2D numerical simulation and experimental data in different operation regions.
Highlights
A significant distinction between junctionless (JL) and inversion mode (IM) of polysilicon thin-film transistors is that the channel of JL device is heavily doped of the same type and a similar magnitude of concentration as the source and the drain
Model based on charge density5 has been developed for JL symmetric double-gate (SDG) MOSFETs, which applies a coarse finite-different approximation
For a SDG JL MOSFET, Taur et al.6 proposed a physical relation between surface potential and potential at the center film for a given gate voltage, but an explicit solution cannot be obtained
Summary
A significant distinction between junctionless (JL) and inversion mode (IM) of polysilicon thin-film transistors (poly-Si TFTs) is that the channel of JL device is heavily doped of the same type and a similar magnitude of concentration as the source and the drain It can skip junction formation issues and greatly simplify fabrication. A surface-potential-based model for SDG JL MOSFETs was established, and simplified calculations for surface potential and drain current were carried out in different operation regions. This regional approximation has its limitation, it comes out that the approximations so far are quite accurate and well sounded. Predict the DC characteristics in a wide range of operation regions, i.e., from subthreshold, partial depletion, to accumulation, and from linear to saturation
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